Chemical flooding of oilfields with surfactant and water in order to repressurize them is a known type of tertiary oil recovery. The fluids so produced are emulsions of oil, water, and surfactant. One problem has been separating out the components of the emulsion. It would be desirable to recover as much surfactant as possible from the emulsion for reuse in subsequent flooding operations. Efficient and economical separation of the water from the oil would also be desirable, to facilitate subsequent refining of the oil. Conventional field treatment of such emulsions has included the following: settling, heating or distilling at atmospheric pressure, heating or distilling at elevated pressure, centrifugation (&gt;20,000 rpm), electrical dehydration, and chemical demulsification. Chemical demulsification, which is in wide use, often involves addition of substantial quantities of chemicals, with attendant costs. Further, such chemicals usually need to be tailored for the production from a particular oilfield. A technique for surfactant recovery having wider applicability to emulsions from different fields would be desirable.
Ultrafiltration has been used in laboratory scale studies for the separation of very dilute oil-in-water emulsions such as might be found in seawater after oil spills, not the type of emulsion obtained from an oilfield after chemical flooding. U.S. Department of Transportation, U.S. Coast Guard Study No. 734305.2.